Introduction to version control with Git

Day 2: Branching, Merging and collaboration workflows

Selina Baldauf

September 18, 2023

Before we start

Did everyone accept the invitation to the cook book of their partner?

Recap

Basic Git workflow:

  1. Initialize a Git repository
  2. Work on the project
  3. Stage and commit files to the local repository
  4. Push future changes to the remote repository

Recap

Basic Git workflow:

  1. Initialize a Git repository
  2. Work on the project
  3. Stage and commit files to the local repository
  4. Push future changes to the remote repository

Recap

Git is a distributed version control system

  • Idea: many local repositories synced via one remote repo
  • Collaborate with
    • yourself on different machines
    • your colleagues and friends
    • strangers on open source projects

Get a repo from a remote

  • In Git language, this is called cloning
    • Get a full copy of the remote repo

  • If the clone is authorized it can also commit and push

Now you

Clone your partners cookBook repo Complete task 1 “Clone” (5 min)

Get changes from the remote

  • Local changes, publish to remote: git push

  • Remote changes, pull to local: git pull

A simple collaboration workflow


  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the same branch
    • Pull before you start working
    • Push after you finished working

A simple collaboration workflow


This works well if

  • Repo is not updated often
  • You don’t work on the same files simultaneously
  • No need to discuss changes
    • Everything is directly integrated in main
  • You collaborate with yourself

A simple collaboration workflow


This workflow starts to be problematic when

  • People push often
    • Conflicts on main
  • Not possible to discuss code before integration
  • Difficult to just “try something out”
    • Everything goes directly to main

Let’s give it a try

  • Open a recipe in the cook book of your partner
  • Change something in there
  • Commit the change and push it
  • Now switch to your own cook book
  • Pull the change that your partner just did
  • Checkout what they changed in the history tab

A branching-merging workflow


  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge your branch with the main when you are finished

A branching-merging workflow


Advantages of this approach

  • Guarantee that main always works
  • Potential conflicts don’t have to be solved on main
  • You can just “try something out”

Working on a separate branch

The steps to create and work on a separate branch are easy:

  • Create a local branch and switch to it
  • Work on the branch like you are used to
    • Make changes, stage and commit, publish and push

Merging changes from a branch

To bring changes to the main branch you need to merge them.

Normally: Git merge brings the commits from the branch to main

Merging changes from a branch

To bring changes to the main branch you need to merge them.

If there was a commit on a common file in main, a merge commit is introduced.

Merging changes from a branch

To bring changes to the main branch you need to merge them.

  • Mostly merging happens without problems, but…
  • … if the same line was edited on separate branches…
  • … there will be a merge conflict 😱

Merge conflicts need to be solved manually. You need to chose which of the conflicting versions you want to keep.

Now you

Create a branch in your partner’s cook book Complete task 2 “Branch and merge” (10 min)

Before we continue

You partner now has pushed some changes to your cook book.

Get the changes from the remote. In Github Desktop

  • Switch to your own cook book repository
  • Click the pull button (same as push)
  • Have a look at the commit history to see your partner’s changes

A branching-merging workflow with Github

  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge your branch with the main when you are finished

A branching-merging workflow with Github

  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge your branch with the main when you are finished
    • Create a pull request on Github to ask for a merge

A branching-merging workflow with Github

A pull request is basically asking your collaborators:

What do you think of my changes? Can we integrate them in main or do we still need to change something?

Github has nice features for pull requests:

  • Describe your changes in detail
  • Collaborators can easily compare versions
  • Collaborators can discuss and comment on your changes
  • …

A branching-merging workflow with Github

A pull request is basically asking your collaborators:

What do you think of my changes? Can we integrate them in main or do we still need to change something?

A pull request is merged on Github when everyone agreed on the code.

Now you

Create a pull request on your partners repo Review the pull request by your partner on your own repo Complete task “Pull requests” (20 min)

Thanks for your attention

Questions?

Next week

Idea: Questions and problems often arise when working with the tool.

Until then

Work with Git (~ 2 h), e.g.

  • Start using version control for you own projects
  • Create a cook book project using the terminal
  • Try to use Git from R (see How-To)
  • …

Write down your problems/questions/other Git things you are interested in.

Next week we will - Discuss your questions - Look at other interesting Git things todo - e.g. Use Git from R, VS Code - Use Github to publish websites - …

Branching, Merging and Collaboration with Git